Long queues are delaying drivers on the A27 in Chichester around the Bognor Bridge roundabout in both directions.
Further east, along Bognor Road, traffic is queuing eastbound.
Along the A27, queues are also tailing back from The White Swan Inn near Arundel, getting worse eastbound into Worthing.
In Worthing, traffic is backed up along the A24 and A27 around the Grove Lodge roundabout as construction around the north of the town continues to bring disruption.
Motorists are caught in westbound gridlock from the Manor roundabout back further than the Holmbush turn-off.
In East Sussex, traffic is queuing along the A259 in Newhaven, adding around 15 minutes to journeys.
Long delays along the A27 are reported at Polegate in the construction area at the Cop Hall roundabout.
North of Hastings, traffic is queuing along the A21 from Beauport Holiday Park.